Method and device for encoding/decoding multi-layer video signal

ABSTRACT

A method for decoding a multi-layer video signal, according to the present invention, determines whether a corresponding picture in a lower layer is used as an inter-layer reference picture for a current picture in an upper layer, on the basis of a time level identifier of the lower layer, and restrictively performs inter-layer prediction for the current picture on the basis of a tile boundary alignment flag indicating whether tile alignment is performed between the upper layer and the lower layer if the corresponding picture in the lower layer is used as the inter-layer reference picture for the current picture in the upper layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Patent Application of PCTInternational Patent Application No. PCT/KR2014/009880 (filed on Oct.21, 2014) under 35 U.S.C. § 371, which claims priority to Korean PatentApplication No. 10-2013-0125922 (filed on Oct. 22, 2013), the teachingsof which are incorporated herein in their entireties by reference.

TECHNICAL FIELD

The present invention relates to a method and apparatus forencoding/decoding a multi-layer video signal.

BACKGROUND ART

Demands for high-resolution, high-quality images such as High Definition(HD) images and Ultra High Definition (UHD) images have recentlyincreased in various fields of applications. As video data has a higherresolution and higher quality, the video data is larger in amount thantraditional video data. Therefore, if video data is transmitted on anexisting medium such as a wired/wireless wideband circuit or stored inan existing storage medium, transmission cost and storage cost increase.To avert these problems encountered with higher-resolution,higher-quality video data, high-efficiency video compression techniquesmay be used.

There are a variety of video compression techniques includinginter-picture prediction in which pixel values included in a currentpicture are predicted from a picture previous to or following thecurrent picture, intra-picture prediction in which pixel values includedin a current picture are predicted using pixel information in thecurrent picture, and entropy encoding in which a short code is assignedto a more frequent value and a long code is assigned to a less frequentvalue. Video data may be compressed effectively and transmitted orstored, using such a video compression technique.

Along with the increasing demands for high-resolution videos, demandsfor three-dimensional (3D) video content as a new video service havebeen increasing. A video compression technique for effectively providingHD and UHD 3D video content is under discussion.

DISCLOSURE Technical Problem

An object of the present invention is to provide a method and apparatusfor determining an inter-layer reference picture for a current pictureof an upper layer in encoding/decoding a multi-layer video signal.

Another object of the present invention is to provide a method andapparatus for up-sampling a picture of a lower layer inencoding/decoding a multi-layer video signal.

Another object of the present invention is to provide a method andapparatus for effectively inducing texture information of an upper layerthrough inter-layer prediction in encoding/decoding a multi-layer videosignal.

Another object of the present invention is to provide a method andapparatus for performing inter-layer prediction based on inter-layertile alignment in encoding/decoding a multi-layer video signal.

Technical Solution

In a method and apparatus for decoding a multi-layer video signalaccording to the present invention, it may be determined whether acorresponding picture of a lower layer is used in inter-layer predictionof a current picture of an upper layer, based on a temporal levelidentifier (ID) of the lower layer, and if the corresponding picture ofthe lower layer is used in inter-layer prediction of the current pictureof the upper layer, inter-layer prediction of the current picture may beperformed using the corresponding picture.

In the method and apparatus for decoding a multi-layer video signalaccording to the present invention, the inter-layer prediction may beperformed restrictively depending on a tile boundary alignment flagindicating whether tiles between the upper layer and the lower layer arealigned.

In the method and apparatus for decoding a multi-layer video signalaccording to the present invention, if the tile boundary alignment flaghas a value of 1, when two samples of the current picture belonging tothe upper layer belong to one tile, two samples of the correspondingpicture belonging to the lower layer may belong to one tile, and whenthe two samples of the current picture belonging to the upper layerbelong to different tiles from each other, the two samples of thecorresponding picture belonging to the lower layer may belong todifferent tiles from each other.

In the method and apparatus for decoding a multi-layer video signalaccording to the present invention, if the tile boundary alignment flagis 1, a sample outside the tile belonging to the corresponding pictureis not used for the inter-layer prediction of a sample inside the tilebelonging to the current picture.

In the method and apparatus for decoding a multi-layer video signalaccording to the present invention, the tile boundary alignment flag maybe acquired restrictively based on the number of a tile belonging to thecurrent picture.

In a method and apparatus for encoding a multi-layer video signalaccording to the present invention, it may be determined whether acorresponding picture of a lower layer is used in inter-layer predictionof a current picture of an upper layer, based on a temporal level ID ofthe lower layer, and if the corresponding picture of the lower layer isused in inter-layer prediction of the current picture of the upperlayer, inter-layer prediction of the current picture may be performedusing the corresponding picture.

In the method and apparatus for encoding a multi-layer video signalaccording to the present invention, the inter-layer prediction may beperformed restrictively depending on a tile boundary alignment flagindicating whether tiles between the upper layer and the lower layer arealigned.

In the method and apparatus for encoding a multi-layer video signalaccording to the present invention, if the tile boundary alignment flaghas a value of 1, when two samples of the current picture belonging tothe upper layer belong to one tile, two samples of the correspondingpicture belonging to the lower layer may belong to one tile, and whenthe two samples of the current picture belonging to the upper layerbelong to different tiles from each other, the two samples of thecorresponding picture belonging to the lower layer may belong todifferent tiles from each other.

In method and apparatus for encoding a multi-layer video signalaccording to the present invention, if the tile boundary alignment flaghas a value of 1, a sample outside the tile belonging to thecorresponding picture is not used for the inter-layer prediction of asample inside the tile belonging to the current picture.

In the method and apparatus for encoding a multi-layer video signalaccording to the present invention, the tile boundary alignment flag maybe acquired restrictively based on the number of a tile belonging to thecurrent picture.

Advantageous Effects

According to the present invention, a memory can be managed effectivelyby adaptively using a lower-layer picture as an inter-layer referencepicture for a current upper-layer picture.

According to the present invention, a lower-layer picture can beup-sampled effectively.

According to the present invention, texture information of an upperlayer can be induced effectively through inter-layer prediction.

According to the present invention, the coding efficiency of a videosignal can be increased by restrictively performing inter-layerprediction based on inter-layer tile alignment in a multi-layerstructure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an encoding apparatus accordingto an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a decoding apparatus according toan embodiment of the present invention.

FIG. 3 is a flowchart illustrating an operation for performinginter-layer prediction for an upper layer using a corresponding pictureof a lower layer in an embodiment to which the present invention isapplied.

FIG. 4 is a flowchart illustrating an operation for determining whethera corresponding picture of a lower layer is used as an inter-layerreference picture for a current picture in an embodiment to which thepresent invention is applied.

FIG. 5 is a flowchart illustrating a method for acquiring a maximumtemporal level identifier (ID) by extracting the maximum temporal levelID from a bit stream in an embodiment to which the present invention isapplied.

FIG. 6 illustrates a relationship between slices and tiles in anembodiment to which the present invention is applied.

FIG. 7 is a flowchart illustrating a method for performing inter-layerprediction using tile alignment between multiple layers in an embodimentto which the present invention is applied.

FIG. 8 is a flowchart illustrating a method for adaptively performinginter-layer tile alignment based on a discardable flag in an embodimentto which the present invention is applied.

FIGS. 9, 10, and 11 are flowcharts illustrating methods for adaptivelyperforming inter-layer tile alignment based on a temporal level ID,TemporalID of a lower layer in an embodiment to which the presentinvention is applied.

FIG. 12 is a flowchart illustrating a method for performing restrictedinter-layer prediction depending on inter-layer tile alignment ormisalignment in an embodiment to which the present invention is applied.

FIGS. 13, 14, and 15 illustrate syntaxes of a tile boundary alignmentflag in an embodiment to which the present invention is applied.

FIG. 16 is a flowchart illustrating a method for up-sampling acorresponding picture of a lower layer in an embodiment to which thepresent invention is applied.

BEST MODE FOR CARRYING OUT THE INVENTION

A method and apparatus for decoding a multi-layer video signal accordingto the present invention are characterized in that it is determinedwhether a corresponding picture of a lower layer is used in inter-layerprediction of a current picture of an upper layer, based on a temporallevel identifier (ID) of the lower layer, and if the correspondingpicture of the lower layer is used in inter-layer prediction of thecurrent picture of the upper layer, inter-layer prediction of thecurrent picture is performed using the corresponding picture.

The method and apparatus for decoding a multi-layer video signalaccording to the present invention are characterized in that theinter-layer prediction is performed restrictively depending on a tileboundary alignment flag indicating whether tiles between the upper layerand the lower layer are aligned.

The method and apparatus for decoding a multi-layer video signalaccording to the present invention are characterized in that, if thetile boundary alignment flag has a value of 1, when two samples of thecurrent picture belonging to the upper layer belong to one tile, twosamples of the corresponding picture belonging to the lower layer belongto one tile, and when the two samples of the current picture belongingto the upper layer belong to different tiles from each other, the twosamples of the corresponding picture belonging to the lower layer belongto different tiles from each other.

The method and apparatus for decoding a multi-layer video signalaccording to the present invention are characterized in that if the tileboundary alignment flag is 1, a sample outside the tile belonging to thecorresponding picture is not used for the inter-layer prediction of asample inside the tile belonging to the current picture.

The method and apparatus for decoding a multi-layer video signalaccording to the present invention are characterized in that the tileboundary alignment flag is acquired restrictively based on the number ofa tile belonging to the current picture.

A method and apparatus for encoding a multi-layer video signal accordingto the present invention are characterized in that it is determinedwhether a corresponding picture of a lower layer is used in inter-layerprediction of a current picture of an upper layer, based on a temporallevel ID of the lower layer, and if the corresponding picture of thelower layer is used in inter-layer prediction of the current picture ofthe upper layer, inter-layer prediction of the current picture isperformed using the corresponding picture.

The method and apparatus for encoding a multi-layer video signalaccording to the present invention are characterized in that theinter-layer prediction is performed restrictively depending on a tileboundary alignment flag indicating whether tiles between the upper layerand the lower layer are aligned.

The method and apparatus for encoding a multi-layer video signalaccording to the present invention are characterized in that, if thetile boundary alignment flag has a value of 1, when two samples of thecurrent picture belonging to the upper layer belong to one tile, twosamples of the corresponding picture belonging to the lower layer belongto one tile, and when the two samples of the current picture belongingto the upper layer belong to different tiles from each other, the twosamples of the corresponding picture belonging to the lower layer belongto different tiles from each other.

The method and apparatus for encoding a multi-layer video signalaccording to the present invention are characterized in that if the tileboundary alignment flag has a value of 1, a sample outside the tilebelonging to the corresponding picture is not used for the inter-layerprediction of a sample inside the tile belonging to the current picture.

The method and apparatus for encoding a multi-layer video signalaccording to the present invention are characterized in that the tileboundary alignment flag is acquired restrictively based on the number ofa tile belonging to the current picture.

MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be described belowin detail with reference to the attached drawings. Before the detaileddescription, it is to be understood that terms or words as used in thepresent disclosure and the claims should be interpreted not as theirgeneral or dictionary meanings but as meanings and concepts matching thescope and spirit of the present invention based on the principle thatthe inventor can define the concepts of terms appropriately in the bestmanner. Therefore, the embodiments as described below and configurationsshown in the drawings are merely preferred embodiments of the presentinvention, not representing all of the technical subject matter of thepresent invention. Accordingly, it is to be understood that they can bereplaced with various equivalents and modification examples at the timeof filing the present invention.

When it is said that a component is “coupled with/to” or “connected to”another component, it should be understood that the one component iscoupled or connected to the other component directly or through anyother component in between. In the present disclosure, the term“include” does not exclude the presence of any other component than aspecific component, meaning that an additional component may be includedin an embodiment of the present invention or the scope of the presentinvention.

The term as used in the present disclosure, first or second may be usedto describe various components, not limiting the components. Theseexpressions are used to distinguish one component from anothercomponent. For example, a first component may be referred to as a secondcomponent and vice versa without departing the scope of the presentdisclosure.

Also, components in embodiments of the present invention are shown asindependent to illustrate different characteristic functions, notmeaning that each component is configured in a separate hardware unit orone software unit. That is, each component is enumerated separately, forthe convenience of description. Thus, two or more components may beincorporated into one component or one component may be divided into aplurality of components. An embodiment of integrating components and anembodiment of dividing a component fall into the scope of the presentinvention.

Some components may be optional to increase performance, not essentialto main functions of the present invention. The present invention may beimplemented only with components essential to the subject matter of thepresent invention, without components used just to increase performance,which falls within the scope of the present invention.

Video encoding and decoding that supports multiple layers of a bitstream is called scalable video coding. Because there is a strongcorrelation between the multiple layers, redundant components of datamay be eliminated and video coding performance may be increased, byperforming prediction based on the correlation. Prediction of a currentlayer using information about another layer is referred to asinter-layer prediction.

The multiple layers may have different resolutions. The resolutions maymean at least one of spatial resolution, temporal resolution, and imagequality. To control resolution during inter-layer prediction, a layermay be subjected to re-sampling such as up-sampling or down-sampling.

FIG. 1 is a block diagram schematically illustrating an encoding deviceaccording to an embodiment of the present invention.

An encoding device 100 according to the present invention includes anencoding unit 100 a for an upper layer and an encoding unit 100 b for alower layer.

The upper layer may be called a current layer or an enhancement layer,and the lower layer may be called an enhancement layer having resolutionlower than that of the upper layer, a base layer or a reference layer.At least one of the spatial resolution, temporal resolution based on aframe rate, color format, and image quality based on a quantization stepsize may differ between the upper layer and the lower layer. When achange of resolution is required for inter-layer prediction, up-samplingor down-sampling of the layer may be performed.

The encoding unit 100 a for the upper layer may include a partitioningunit 110, a prediction unit 120, a transform unit 130, a quantizationunit 140, a rearrangement unit 150, an entropy coding unit 160, aninverse quantization unit 170, an inverse-transform unit 180, a filterunit 190, and memory 195.

The encoding unit 100 b for the lower layer may include a partitioningunit 111, a prediction unit 125, a transform unit 131, a quantizationunit 141, a rearrangement unit 151, an entropy coding unit 161, aninverse quantization unit 171, an inverse-transform unit 181, a filterunit 191, and memory 196.

The encoding unit may be implemented by a video encoding methoddescribed in an embodiment of the present invention, which will bedescribed below, but the operations of some parts may not be performedin order to reduce the complexity of the encoding device or to enablefast real-time encoding. For example, rather than a method in which allintra-prediction mode methods are used to select the optimalintra-encoding method, a method in which one is selected from among alimited number of intra-prediction modes and the selected one is set asthe final intra-prediction mode may be performed for real-time encodingwhen the prediction unit performs intra-prediction. In another example,a prediction block used for intra-prediction or inter-prediction mayhave a limited shape.

The unit of a block processed in the encoding device may be a codingunit for performing coding, a prediction unit for performing prediction,or a transform unit for performing transformation. The coding unit, theprediction unit, and the transform unit may be represented as CU, PU,and TU, respectively.

Each of the partitioning units 110 and 111 may partition a layer bypartitioning a layer picture into multiple combinations of codingblocks, prediction blocks, and transform blocks, and by selecting onecombination of coding blocks, prediction blocks, and transform blocksbased on a predetermined reference (for example, a cost function). Forexample, in order to partition a layer picture into coding units, arecursive tree structure such as a QuadTree structure may be used.Hereinafter, in an embodiment of the present invention, a coding blockmay mean not only a block for encoding but also a block for decoding.

A prediction block may be a unit for performing prediction, such asintra-prediction or inter-prediction. A block for intra-prediction maybe a block having the form of a square, such as 2N×2N or N×N. As a blockfor inter-prediction, there are a block in the form of a square, such as2N×2N and N×N, a block in the form of a rectangle, such as 2N×N andN×2N, and a block having an asymmetric form, obtained by a predictionblock partitioning method using Asymmetric Motion Partitioning (AMP).The transform unit 115 may use different transform methods depending onthe form of the prediction block.

Each of the prediction units 120 and 125 of the encoding units 100 a and100 b may include an intra-prediction unit 121 or 126 for performingintra-prediction and an inter-prediction unit 122 or 127 for performinginter-prediction. The prediction unit 120 of the encoding unit 100 a forthe upper layer may further include an inter-layer prediction unit 123,which performs prediction of the upper layer using the informationrelating to the lower layer.

Each of the prediction units 120 and 125 may determine whether toperform inter-prediction or intra-prediction of a prediction block. Whenintra-prediction is performed, an intra-prediction mode is determinedbased on a prediction block, and a process for processingintra-prediction based on the determined intra-prediction mode may beperformed based on a transform block. A residual (residual block)between the generated prediction block and the original block may beinput to the transform units 130 and 131. Also, the prediction modeinformation used for prediction, motion information, and the like areencoded along with the residual by the entropy coding unit 130, and maybe transmitted to the decoding device.

When a Pulse Code Modulation (PCM) mode is used, the original block maybe encoded unchanged without performing prediction using the predictionunits 120 and 125, and may be transmitted to a decoding unit.

Each of the intra-prediction units 121 and 126 may generate anintra-predicted block based on reference pixels located around thecurrent block (the prediction target block). In the intra-predictionmethod, the intra-prediction mode may have a directional predictionmode, which uses reference pixels according to the prediction direction,and a non-directional mode, which does not consider a predictiondirection. The mode for predicting luma information may be differentfrom the mode for predicting chroma information. Intra-prediction mode,obtained by predicting luma information, or the predicted lumainformation may be used to predict chroma information. Meanwhile, if thereference pixels are not available, a prediction block may be generatedby replacing the unavailable reference pixels with other pixels.

A prediction block may include multiple transform blocks. If the size ofa prediction block is the same as the size of a transform block whenperforming intra-prediction, intra-prediction of the prediction blockmay be performed based on a left pixel, an upper-left pixel, and anupper pixel of the prediction block. However, as the time ofintra-prediction, when the sizes of the prediction block and thetransform block are different and multiple transform blocks are includedinside the prediction block, neighboring pixels adjacent to thetransform blocks are used as reference pixels to perform theintra-prediction. Here, the neighboring pixels adjacent to the transformblock may include at least one of neighboring pixels adjacent to theprediction block and previously decoded pixels in the prediction blocks.

However, if the size of a prediction block is different from that of atransform block when performing intra-prediction and thus the predictionblock includes multiple transform blocks, intra-prediction may beperformed based on reference pixels determined based on the transformblock.

The intra-prediction method may generate a prediction block afterapplying a Mode-Dependent Intra Smoothing (MDIS) filter to referencepixels according to the intra-prediction mode. The type of MDIS filterapplied to the reference pixels may vary. The MDIS filter is anadditional filter applied to an intra-predicted block generated byperforming intra-prediction, and may be used for reducing a residualbetween reference pixels and the intra-predicted block, generated afterperforming prediction. When MDIS filtering is performed, differentfiltering may be performed on reference pixels and on some columnsincluded in the intra-predicted block according to the direction of theintra-prediction mode.

Each of the inter-prediction units 122 and 127 may perform prediction byreferring to the information about a block included in at least one ofthe picture preceding and the picture following the current picture.Each of the inter-prediction units 122 and 127 may include a referencepicture interpolation unit, a motion prediction unit, and a motioncompensation unit.

The reference picture interpolation unit may receive reference pictureinformation from memory 195 or 196 and may generate information about apixel, which is smaller than an integer pixel, from the referencepicture. For a luma pixel, a DCT-based 8-tap interpolation filter, whichdifferently sets filter coefficients to generate information about apixel that is smaller than an integer pixel in units of ¼ pixels, may beused. For chroma signals, a DCT-based 4-tap interpolation filter, whichdifferently sets filter coefficients to generate information about apixel that is smaller than an integer pixel in units of ⅛ pixels, may beused.

Each of the inter-prediction units 122 and 127 may perform motionprediction based on the reference picture interpolated by the referencepicture interpolation unit. As a method for calculating a motion vector,various methods, such as a Full search-based Block Matching Algorithm(FBMA), a Three-Step Search (TSS) algorithm, and a New Three-Step Search(NTS) Algorithm, may be used. The motion vector may have a motion vectorvalue corresponding to ½ or ¼ of the interpolated pixel. Each of theinter-prediction units 122 and 127 may perform prediction on a currentblock using any one of various inter-prediction methods.

As the inter-prediction method, any of various methods such as a skipmethod, a merge method, and a Motion Vector Prediction (MVP) method maybe used.

In inter-prediction, motion information, that is, information about areference index, a motion vector, and a residual signal, isentropy-coded and then transferred to the decoding unit. When a skipmode is applied, a residual signal is not generated, and thus aprocedure for transforming and quantizing a residual signal may beomitted.

The inter-layer prediction unit 123 performs inter-layer prediction forpredicting an upper layer using information about the lower layer. Theinter-layer prediction unit 123 may perform inter-layer prediction usingthe texture information, motion information, etc. of the lower layer.

The inter-layer prediction may be performed by setting the picture ofthe lower layer as a reference picture and performing prediction on thecurrent block of the upper layer using the motion information in thepicture of the lower layer (reference layer). The picture of thereference layer, used as a reference picture in the inter-layerprediction, may be a picture that is sampled so as to match theresolution of the current layer. Also, the motion information mayinclude a motion vector and a reference index. In this case, the motionvector value for the picture of the reference layer may be set to (0,0).

As an example of the inter-layer prediction, a prediction method thatuses the picture of a lower layer as a reference picture is described,but the present invention is not limited to this. The inter-layerprediction unit 123 may additionally perform inter-layer textureprediction, inter-layer motion prediction, inter-layer syntaxprediction, inter-layer residual prediction, and the like.

The inter-layer texture prediction may derive the texture of the currentlayer based on the texture of the reference layer. The texture of thereference layer may be sampled to match the resolution of the currentlayer, and the inter-layer prediction unit 123 may predict the textureof the current layer based on the sampled texture of the referencelayer.

The inter-layer motion prediction may derive the motion vector of thecurrent layer based on the motion vector of the reference layer. In thiscase, the motion vector of the reference layer may be scaled to matchthe resolution of the current layer. The inter-layer syntax predictionmay predict the syntax of the current layer based on the syntax of thereference layer. For example, the inter-layer prediction unit 123 mayuse the syntax of the reference layer as the syntax of the currentlayer. Also, the inter-layer residual prediction may reconstruct thepicture of the current layer using the residual between the restoredpicture of the reference layer and the restored picture of the currentlayer.

A residual block including residual information, which is the differencebetween the prediction block generated by each of the prediction units120 and 125 and the reconstructed block of the prediction block, isgenerated, and the residual block is input to the correspondingtransform unit 130 or 131.

Each of the transform units 130 and 131 may transform the residual blockusing a transform method such as a Discrete Cosine Transform (DCT) orDiscrete Sine Transform (DST). Whether to apply DCT or DST to transformthe residual block may be determined based on the intra-prediction modeinformation of the prediction block used to generate the residual blockand the size information of the prediction block. That is, each of thetransform units 130 and 131 may use different transform methodsdepending on the size of the prediction block and the prediction method.

Each of the quantization units 140 and 141 may quantize valuestransformed in the frequency domain by the corresponding transform unit130 or 131. The quantization coefficients may change depending on thetype of block or the importance of the pictures. The value calculated bythe quantization unit 140 or 141 may be provided to theinverse-quantization unit 170 or 17 and the rearrangement unit 150 or151.

Each of the rearrangement units 150 and 151 may rearrange coefficientvalues of the quantized residual value. The rearrangement unit 150 or151 may change a 2D block format coefficient to a 1D vector formatcoefficient using a coefficient scanning method. For example, therearrangement unit 150 or 151 may change the 2D block format coefficientto a 1D vector format coefficient by scanning coefficients ranging froma DC coefficient to a high-frequency band coefficient using a zigzagscanning method. Depending on the size of the transform block and on theintra-prediction mode, a vertical scanning method for scanning 2D blockformat coefficients in a column direction and a horizontal scanningmethod for scanning 2D block format coefficients in a row direction,rather than the zigzag scanning method, may be used. That is, thedetermination of which one of the zigzag scanning, vertical scanning,and horizontal scanning methods is to be used may be made depending onthe size of the transform block and the intra-prediction mode.

Each of the entropy coding units 160 and 161 may perform entropy codingbased on the values calculated by the rearrangement unit 150 or 151. Theentropy coding may be implemented using, for example, various codingmethods such as Exponential Golomb, Context-Adaptive Variable LengthCoding (CAVLC), and Context-Adaptive Binary Arithmetic Coding (CABAC).

The entropy coding units 160 and 161 may perform entropy coding based ona predetermined coding method by receiving various information, such asresidual coefficient information and block type information of a codingblock, prediction mode information, partition unit information,prediction block information and transmission unit information, motionvector information, reference frame information, interpolationinformation for a block, filtering information, and the like, from therearrangement units 150 and 151 and the prediction units 120 and 125.Also, the entropy coding units 160 and 161 may entropy-code thecoefficient value of a coding unit, input from the rearrangement units150 and 151.

Each of the entropy coding units 160 and 161 may encode theintra-prediction mode information of the current block by binary-codingthe intra-prediction mode information. The entropy coding units 160 and161 may include a codeword mapping unit for the binary coding, and mayperform the binary coding differently depending on the size of theprediction block for intra-prediction. The codeword mapping unit mayadaptively generate a codeword mapping table through a binary codingoperation, or may have a previously generated mapping table. In anotherembodiment, the entropy coding units 160 and 161 may represent theintra-prediction mode information about the current block using acode-num mapping unit for performing code-num mapping and a codewordmapping unit for performing codeword mapping. The code-num mapping unitand the codeword mapping unit may generate a code-num mapping table anda codeword mapping table, respectively, or may respectively have apreviously generated code-num mapping table and codeword mapping table.

Each of the inverse quantization units 170 and 171 and the inversetransform unit 180 or 181 may inverse-quantize the values quantized bythe quantization unit 140 or 141 and inverse-transform the valuestransformed by the transform unit 130 or 131. The residual valuegenerated by the inverse quantization unit 170 or 171 and the inversetransform unit 180 or 181 may be combined with the prediction blockpredicted by the motion estimation unit, the motion compensation unit,and the intra-prediction unit, which are included in the prediction unit120 or 125, and thus a reconstructed block may be generated.

Each of the filter units 190 and 191 may include at least one of adeblocking filter and an offset correction unit.

The deblocking filter may remove block distortion, generated due to theboundaries between blocks, in the reconstructed picture. Whether toperform deblocking, namely, whether to apply the deblocking filter tothe current block, may be determined based on the pixels included insome rows or columns of the block. When the deblocking filter is appliedto a block, a strong filter or a weak filter may be applied according tothe required strength of deblocking filtering. Also, in applying thedeblocking filter, when vertical filtering and horizontal filtering areperformed, the vertical filtering and the horizontal filtering may beprocessed in parallel.

The offset correction unit may correct an offset between the picture onwhich deblocking is performed and the original picture in pixel units.In order to perform the offset correction on a specific picture, amethod in which the pixels included in the picture are divided intocertain areas, the area to which an offset is to be applied isdetermined, and the offset is applied to the area may be used, or amethod in which the offset is applied in consideration of theinformation about the edge of each pixel may be used.

Each of the filter units 190 and 191 may be implemented using only adeblocking filter, or using both a deblocking filter and offsetcorrection, rather than using all of a deblocking filter and offsetcorrection.

Each of the memory 195 and 196 may store the reconstructed block orpictures calculated by the filter unit 190 or 191, and the reconstructedblock and pictures stored in the memory may be provided to theprediction unit 120 or 125 when intra-prediction is performed.

Information output from the entropy coding unit 100 b of the lower layerand information output from the entropy coding unit 100 a of the upperlayer are multiplexed by the MUX 197, and may then be output in the formof a bitstream.

The MUX 197 may be included in the encoding unit 100 a of the upperlayer or the encoding unit 100 b of the lower layer, or may beimplemented as a separate device or module, unlike the encoding unit100.

FIG. 2 is a block diagram schematically showing a decoding deviceaccording to an embodiment of the present invention.

As shown in FIG. 2, a decoding device 200 includes a decoding unit 200 aof an upper layer and a decoding unit 200 b of a lower layer.

The decoding unit 200 a of the upper layer may include an entropydecoding unit 210, a rearrangement unit 220, an inverse-quantizationunit 230, an inverse-transform unit 245, a prediction unit 250, a filterunit 260, and memory 270.

The decoding unit 200 b of the lower layer may include an entropydecoding unit 211, a rearrangement unit 221, an inverse-quantizationunit 231, an inverse-transform unit 241, a prediction unit 251, a filterunit 261, and memory 271.

When a bitstream including multiple layers is transmitted from theencoding device, a demultiplexer (DEMUX) 280 demultiplexes theinformation corresponding to each of the layers and transmits the resultto the decoding unit 200 a or 200 b of each of the layers. The inputbitstream may be decoded through a process that is the reverse of theprocess of the encoding device.

Each of the entropy decoding units 210 and 211 may performentropy-decoding through the reverse of the entropy-coding processperformed by the entropy coding unit of the encoding device. Among thepieces of information decoded by the entropy decoding units 210 and 211,information required to generate a prediction block is provided to theprediction units 250 and 251, and a residual, entropy-decoded by theentropy decoding unit, may be input to the rearrangement units 220 and221.

Each of the entropy decoding units 210 and 211 may use at least one ofCABAC and CAVLC, like the entropy coding units 160 and 161.

Each of the entropy decoding units 210 and 211 may decode informationabout intra-prediction and inter-prediction performed by the encodingdevice. Each of the entropy decoding units 210 and 211 includes acodeword mapping unit that has a codeword mapping table for generatingan intra-prediction mode number from a received codeword. The codewordmapping table may be stored in advance, or may be generated adaptively.When a codeNum mapping table is used, a codeNum mapping unit forperforming codeNum mapping may be additionally arranged.

Each of the rearrangement units 220 and 221 may rearrange the bitstream,entropy-decoded by the entropy decoding unit 210 or 211, based on thearrangement method used by the encoding unit. The coefficients,represented in one-dimensional vector form, may be rearranged as2-dimensional block-type coefficients by being reconstructed. Each ofthe rearrangement units 220 and 221 receives the information about thecoefficient scanning method performed by the encoding unit, and mayrearrange the coefficients using a method in which inverse scanning isperformed based on the sequence of scanning performed by the encodingunit.

Each of the inverse-quantization units 230 and 231 may perform inversequantization based on the quantization parameter provided by theencoding device and the rearranged coefficients of the block.

Each of the inverse-transform units 240 and 241 may perform inverse DCTor inverse DST, which correspond to DCT and DST performed by thecorresponding transform unit 130 or 131, on the result of quantizationperformed by the encoding device. The inverse-transform may be performedin transmission units determined by the encoding device. In thetransform unit of the encoding device, DCT and DST may be selectivelyperformed according to multiple pieces of information, such as theprediction method, the size of the current block, the predictiondirection, and the like. The inverse-transform unit 240 or 241 of thedecoding device may perform inverse transform based on the informationabout the transform performed by the transform unit of the encodingdevice. Transform may be performed based on a coding block rather than atransform block.

Each of the prediction units 250 and 251 may generate a prediction blockbased on information about the generation of the prediction block,provided by the entropy decoding units 210 and 211, and informationabout previously decoded blocks or pictures, provided from thecorresponding memory 270 or 271.

Each of the prediction units 250 and 251 may include a prediction unitdetermination unit, an inter-prediction unit, and an intra-predictionunit.

The prediction unit determination unit receives various information,including prediction unit information input from the entropy decodingunit, prediction mode information about an intra-prediction method,motion prediction information about an inter-prediction method, and thelike, separates a prediction block from a current coding block, anddetermines whether the prediction block performs intra-prediction orinter-prediction.

The inter-prediction unit may perform inter-prediction of the currentprediction block based on information included in at least one of thepicture preceding and the picture following the current picture, whichincludes the current prediction block, using information required forinter-prediction of the current prediction block provided by theencoding device. In order to perform inter-prediction, it may bedetermined whether the method used as the motion prediction method ofthe prediction block included in the coding block based on thecorresponding coding block is a skip mode, a merge mode, or a mode (AMVPmode) using a Motion vector Predictor (MVP).

The intra-prediction unit may generate a prediction block based oninformation about reconstructed pixels in the current picture. When theprediction block is a prediction block on which intra-prediction isperformed, intra-prediction may be performed based on theintra-prediction mode information about the prediction block, providedby the encoding device. The intra-prediction unit may include an MDISfilter for performing filtering on reference pixels of the currentblock, a reference pixel interpolation unit for generating referencepixels in units smaller than a single pixel by interpolating thereference pixels, and a DC filter for generating a prediction blockthrough filtering when the prediction mode of the current block is a DCmode.

The prediction unit 250 of the decoding unit 200 a of the upper layermay further include an inter-layer prediction unit for performinginter-layer prediction, in which the upper layer is predicted usinginformation about the lower layer.

The inter-layer prediction unit may perform inter-layer prediction byusing intra-prediction mode information, motion information, etc.

The inter-layer prediction is implemented such that prediction of acurrent block of the upper layer is performed by adopting a lower layerpicture as a reference picture and using motion information relating tothe picture of the lower layer (reference layer).

In the inter-layer prediction, a picture of the reference layer, whichis used as a reference picture, may be sampled suitably for theresolution of a current layer. In addition, the motion information mayinclude the motion vector and reference index. At this point, a motionvector value for the reference layer picture may be set to (0, 0).

As an example of the inter-layer prediction, a prediction method forusing the lower layer picture as a reference picture is described, butis not limited thereto. The inter-layer prediction unit 123 mayadditionally perform an inter-layer texture prediction, an inter-layermotion prediction, an inter-layer syntax prediction, and an inter-layerresidual prediction, etc.

The inter-layer texture prediction may derive texture of a current layerbased on texture of the reference layer. The reference layer texture maybe sampled suitably for the resolution of the current layer, and theinter-layer prediction unit may predict the current layer texture basedon the sampled texture. The inter-layer motion prediction may derive amotion vector of the current layer based on the motion vector of thereference layer. Here, the motion vector of the reference layer may bescaled suitably for the resolution of the current layer. In theinter-layer syntax prediction, current layer syntax may be predictedbased on the reference layer syntax. For example, the inter-layerprediction unit 123 may use the reference layer syntax as current layersyntax. In addition, in the inter-layer residual prediction, the pictureof the current layer may be reconstructed by using a difference betweena reconstructed image of the reference layer and a reconstructed imageof the current layer.

The reconstructed block or picture may be provided to each of the filterunits 260 and 261. Each of the filter units 260 and 261 may include adeblocking filter and an offset correcting unit.

Information on whether a deblocking filter is applied to a correspondingblock or picture and information on whether a strong filter or a weakfilter is applied, when the deblocking filter is applied, may bereceived from the encoding device. The deblocking filter of the decodingdevice may receive deblocking filter-related information provided fromthe encoding device and the decoding device may perform deblockingfiltering on a corresponding block.

The offset correction unit may perform offset correction on areconstructed image based on the type of the offset correction andoffset value information applied to an image at the time of coding.

Each of the memories 270 and 271 may store the reconstructed picture orblock to allow them to be used as the reference picture or the referenceblock and may also output the reconstructed picture.

The encoding device and decoding device may perform encoding on threelayers or more, not on two layers, and in this case, the coding unit andthe decoding unit for the upper layer may be provided in plural numbersin correspondence to the number of upper layers.

In scalable video coding (SVC) for supporting a multi-layer structure,there is association between layers. When prediction is performed byusing this association, data duplication elements may be removed andimage coding performance may be improved.

Accordingly, when a picture (i.e. an image) of a current layer (i.e. anenhancement layer) to be encoded/decoded is predicted, inter-layerprediction by using information of another layer may be performed aswell as inter prediction or intra-prediction using information of thecurrent layer.

When the inter layer prediction is performed, prediction samples for thecurrent layer may be generated by using a decoded picture of a referencelayer, which is used for inter-layer prediction, as a reference picture.

In this case, since at least one of the spatial resolution, temporalresolution, and image quality may differ between the current layer andthe reference layer (due to the difference in scalability between thelayers), the decoded picture of the reference layer is resampled to beadapted to the scalability of the current layer, and may then be used asthe reference picture for the inter-layer prediction of the currentlayer. “Resampling” means up-sampling or down-sampling the samples ofthe reference layer picture to match the picture size of the currentlayer picture.

In this specification, the current layer is the layer on which encodingor decoding is performed, and may be an enhancement layer or an upperlayer. The reference layer is the layer that is referred to forinter-layer prediction of the current layer, and may be a base layer ora lower layer. The picture of the reference layer (that is, thereference picture) used for inter-layer prediction of the current layermay be called an inter-layer reference picture or a reference picturebetween layers.

FIG. 3 is a flowchart illustrating an operation for performinginter-layer prediction of an upper layer using a corresponding pictureof a lower layer in an embodiment to which the present invention isapplied.

Referring to FIG. 3, it may be determined whether a correspondingpicture of a lower layer is used in inter-layer prediction of a currentpicture of an upper layer, based on a temporal level ID, TemporalID ofthe lower layer (S300).

For example, if a current picture to be encoded in an enhancement layerhas a low temporal resolution (i.e., the temporal level ID, TemporalIDof the current picture has a small value), the difference between thedisplay orders of the current picture and another already decodedpicture of the enhancement layer is wide. In this case, since the imagecharacteristics of the current picture and the already decoded pictureare highly likely to be different, an up-sampled picture of the lowerlayer, instead of the already decoded picture of the enhancement layer,is highly likely to be used as a reference picture for the currentpicture.

On the other hand, if the current picture to be encoded in theenhancement layer has a high temporal resolution (i.e., the temporallevel ID, TemporalID of the current picture has a large value), thedifference between the display orders of the current picture and anotheralready decoded picture of the enhancement layer is not great. In thiscase, since the image characteristics of the current picture and thealready decoded picture are highly likely to be same, the alreadydecoded picture of the enhancement layer is highly likely to be used asa reference picture for the current picture.

Since when the current picture has a low temporal resolution, theinter-layer prediction method is effective, it is necessary to determinewhether to allow inter-layer prediction. For this purpose, a maximumtemporal level ID of a lower layer for which inter-layer prediction isallowed may be signaled, which will be described in detail withreference to FIG. 4.

Meanwhile, the corresponding picture of the lower layer may refer to apicture located at the same time instant as the current picture of theupper layer. For example, the corresponding picture may be a picturehaving the same Picture Order Count (POD) information as the currentpicture of the upper layer. The corresponding picture may be included inthe same Access Unit (AU) as the current picture of the upper layer.

Also, a video sequence may include a plurality of layers encodedscalably according to a temporal/spatial resolution or a quantizationsize. A temporal level ID may be an ID identifying each of a pluralityof layers encoded scalably according to a temporal resolution.

If it is determined that the corresponding picture of the lower layer isused in inter-layer prediction of the current picture of the upper layerin step S300, inter-layer prediction of the current picture may beperformed using the corresponding picture of the lower layer (S310).

Specifically, inter-layer prediction may be performed in parallel on atile basis of multiple layers through tile alignment between the upperlayer and the lower layer, which will be described with reference toFIGS. 7 to 11.

Or inter-layer prediction of the current picture of the upper layer maybe performed restrictively depending on tile alignment or tilemisalignment between the multiple layers, which will be described withreference to FIGS. 12 to 15.

Meanwhile, if the current picture of the upper layer and thecorresponding picture of the lower layer have different spatialresolutions, the corresponding picture of the lower layer may beup-sampled and used as an inter-layer reference picture for the currentpicture. A method for up-sampling a corresponding picture of a lowerlayer will be described with reference to FIG. 16.

FIG. 4 is a flowchart illustrating an operation for determining whethera corresponding picture of a lower layer is used as an inter-layerreference picture for a current picture in an embodiment to which thepresent invention is applied.

Referring to FIG. 4, a maximum temporal level identifier relating to alower layer is able to be obtained S400.

Here, a maximum temporal level identifier means a maximum value of atemporal level identifier of a lower layer to which an inter-layerprediction of an upper layer is allowed.

A maximum temporal level identifier is able to be derived by a maximumtemporal level indicator which is extracted by a bitstream and isdescribed in detail in FIG. 5. Or, the maximum temporal level identifieris able to be derived based on a pre-defined default temporal levelvalue. For example, a pre-defined default temporal level value may meana maximum value in a pre-determined range in which a maximum temporallevel indicator is included. If a pre-determined range relating to avalue of the maximum temporal level indicator is 0 to 7, the pre-defineddefault temporal level value is able to be derived to 7. This can beapplied when a maximum temporal level indicator is not signaled for eachlayer since maximum temporal level indicators of all layers in the videosequence are equal to each other.

Whether a corresponding picture of a lower layer being used as areference picture of a current picture, is determined by comparing amaximum temporal level identifier obtained at S400 to a temporal levelidentifier of a lower level S410.

For example, if a temporal level indicator of a lower level is greaterthan the maximum temporal level indicator, a corresponding picture ofthe lower layer is not used as an inter-layer reference picture for acurrent picture.

On the other hands, a temporal level identifier of a lower layer is lessthan or equal to the maximum temporal level identifier, correspondingpicture of the lower layer is able to be used as an inter-layerreference picture for a current picture. Namely, an inter-layerprediction of a current picture may be performed using a picture of alower layer whose a temporal level indicator is less than the maximumtemporal level indicator.

FIG. 5 is a flowchart illustrating a method for acquiring a maximumtemporal level identifier (ID) by extracting the maximum temporal levelID from a bit stream in an embodiment to which the present invention isapplied.

An encoder determines an optimal maximum temporal level identifier,decodes it and transmits it to a decoder. At this time, an encoder isable to encode a determined maximum temporal level identifier as it isor encode a value (max_tid_il_ref_pics_plus1, hereinafter called‘maximum temporal level indicator’) calculated by adding 1 to adetermined maximum temporal level identifier.

Referring to FIG. 5, a maximum temporal level indicator relating to alower layer is able to be obtained by a bitstream S500.

Here, a maximum temporal level indicator is able to be obtained as muchas a number of maximum layers allowed in one video sequence. A maximumtemporal level indicator is able to be obtained a video parameter set ofa bitstream.

Concretely, if a value of an obtained maximum temporal level indicatoris 0, it means that a corresponding picture of a lower layer is not usedas an inter-layer reference picture for an upper layer. Here, acorresponding picture of a lower layer may be a picture (non-RandomAccess Picture) other than a random-access picture.

For example, if a maximum temporal level indicator is 0, a picture of ani^(th) layer among a plurality of layers in a video sequence is not usedto a reference picture for an inter-layer prediction of a pictureincluded in an (i+1)^(th) layer.

On the other hands, if a maximum temporal level indicator is greaterthan 0, it means that a corresponding picture, which has a temporallevel identifier greater than a maximum temporal level identifier, of alower layer is not used as an inter-layer reference picture for an upperlayer.

For example, if a maximum temporal level indicator is greater than 0, apicture, which has a temporal level identifier greater than a maximumtemporal level identifier, of an i^(th) layer among a plurality oflayers in a video sequence is not used to a reference picture for aninter-prediction of a picture included in an (i+1)^(th) layer. Namely,if a maximum temporal level indicator is greater than 0, and a pictureincluded in an i^(th) layer among a plurality of layers in a videosequence has a temporal level identifier less than a maximum temporallevel identifier, a picture included in an i^(th) layer is used to areference picture for an inter-layer prediction of a picture included inan (i+1)^(th) layer. Here, a maximum temporal level identifier isderived from a maximum temporal level indicator. For instance, a maximumtemporal level identifier is derived to a value subtracting 1 from amaximum temporal level identifier.

Meanwhile, a maximum temporal level indicator derived at S500 has avalue in a pre-determined range (e.g., 0 to 7). If a value of a maximumtemporal level indicator derived at S500 corresponds to a maximum valuein the pre-determined range, a corresponding picture of a lower layer isable to be used as an inter-layer reference picture for an upper layerregardless of a temporal level identifier (TemporalID) of acorresponding picture of a lower layer.

FIG. 6 illustrates a relationship between slices and tiles in anembodiment to which the present invention is applied.

One picture may be divided into at least one slice. A slice may be abasic unit which may be subjected to entropy decoding independently. Oneslice may include a plurality of slice segments.

Further, one picture may be divided into at least one tile. A tile is asquare area including a plurality of coding tree units, and entropydecoding may be performed on a tile basis. Further, a plurality of tilesmay be decoded simultaneously, that is, in parallel. An encoder mayencode an optimum tile size or tile unit and transmit the encoded tilesize or tile unit to a decoder.

Or inter-layer tile alignment may be performed. That is, the tile sizeor tile unit of the upper layer may be induced based on the tile size ortile unit of the lower layer.

FIG. 6(a) illustrates a case in which one picture is divided into oneindependent slice segment and four dependent slice segments. Anindependent slice segment refers to a slice segment including a slicesegment header, whereas a dependent slice segment refers to a slicesegment without a slice segment header, sharing the header of anindependent slice segment. Also, a slice segment includes a plurality ofcoding tree units, each coding tree unit having a size equal to amaximum size of a coding unit which is a basic unit for video signalprocessing.

Referring to FIG. 6(a), one tile may include a plurality of slicesegments, and one slice segment may exist in one tile. Or a plurality oftiles may exist in one slice.

FIG. 6(b) illustrates a case in which one tile includes two or moreslices. That is, referring to FIG. 6(b), slice 0 may include independentslice segment 0 and dependent slice segment 1, and slice 1 may includeindependent slice segment 1 and dependent slice segment 2. Slice 0 andslice 1 may be included in one tile, tile 0.

FIG. 7 is a flowchart illustrating a method for performing inter-layerprediction using tile alignment between multiple layers in an embodimentto which the present invention is applied.

Referring to FIG. 7, tile alignment between multiple layers may beperformed (S700).

Tile alignment between multiple layers may mean that the tile size ortile unit of an upper layer is induced based on the tile size or tileunit of a lower layer. For example, the tile size or tile unit of theupper layer may be set to the same tile size or tile unit as the lowerlayer. Or when the upper layer is encoded, the tile size or tile unit ofthe upper layer is induced using information about the tile size or tileunit of the lower layer.

A method for aligning tile sizes or tile units between an upper layerand a lower layer will be described with reference to FIGS. 8 to 11.

Referring to FIG. 7, inter-layer prediction may be performed on tiles ofmultiple layers in parallel (S710).

Specifically, if the tile size or tile unit of an upper layer is alignedbased on the tile size or tile unit of the lower layer, one tile of thelower layer may be decoded and then one tile of the upper layer may bedecoded. After a next tile of the lower layer is decoded, a next tile ofthe upper layer may be decoded. As the tile sizes or tile units arealigned between the upper layer and the lower layer in this manner,inter-layer prediction between the upper layer and the lower layer maybe performed in parallel.

On the other hand, if a different tile size or tile unit is set on amulti-layer basis, the upper layer may be decoded after the lower layeris completely decoded.

FIG. 8 is a flowchart illustrating a method for adaptively performinginter-layer tile alignment based on a discardable flag in an embodimentto which the present invention is applied.

Referring to FIG. 8, a discardable flag of a corresponding picture of alower layer may be acquired (S800).

The discardable flag may mean information indicating whether a codedpicture is used as a reference picture or an inter-layer referencepicture during decoding of a following picture according to a decodingorder. That is, if the discardable flag is 1, this means that a codedpicture is not used as a reference picture or an inter-layer referencepicture during decoding of a following picture according to a decodingorder. In this case, the coded picture may be marked as unused forreference, indicating that it is not used as a reference picture, inorder to efficiently manage a Decoded Picture Buffer (DPB). On thecontrary, if the discardable flag is 0, this means that a coded pictureis used as a reference picture or an inter-layer reference pictureduring decoding of a following picture according to a decoding order.

Meanwhile, the discardable flag is not limited to acquisition on apicture basis. Obviously, the discardable flag may be acquired on aslice basis or on a slice segment basis.

The value of the discardable flag acquired in step S800 may be checked(S810).

If the discardable flag is 1, inter-layer tile alignment may not beperformed on a current picture of the upper layer based on the tile sizeor tile unit of a corresponding picture of the lower layer (S820).

On the contrary, if the discardable flag is 0, inter-layer tilealignment may be performed on the current picture of the upper layerbased on the tile size or tile unit of the corresponding picture of thelower layer (S830).

FIGS. 9, 10, and 11 are flowcharts illustrating methods for adaptivelyperforming inter-layer tile alignment based on a temporal level ID,TemporalID of a lower layer in an embodiment to which the presentinvention is applied.

Since the efficiency of inter-layer prediction varies according to atemporal level ID in a multi-layer structure, inter-layer tile alignmentmay be performed adaptively according to the temporal level ID of apicture belonging to a specific layer.

(1) Use of Maximum Temporal Level ID of Lower Layer

Referring to FIG. 9, a maximum temporal level ID of a lower layer may beacquired (S900). A method for acquiring a maximum temporal level ID hasbeen described before with reference to FIG. 5 and thus will not bedescribed in detail herein.

The maximum temporal level ID acquired in step S900 may be compared withthe temporal level ID of a corresponding picture of the lower layer(S910).

If the temporal level ID of the corresponding picture of the lower layeris larger than the maximum temporal level ID of the lower layer in stepS910, the corresponding picture of the lower layer may not be used as aninter-layer reference picture for a current picture of an upper layer.Therefore, inter-layer tile alignment may not be performed on thecurrent picture of the upper layer based on the corresponding picture ofthe lower layer (S920).

On the contrary, if the temporal level ID of the corresponding pictureof the lower layer is equal to or less than the maximum temporal levelID of the lower layer in step S910, the corresponding picture of thelower layer may be used as an inter-layer reference picture for thecurrent picture of the upper layer. Therefore, inter-layer tilealignment may be performed on the current picture of the upper layerbased on the corresponding picture of the lower layer (S930).

(2) Use of Temporal Level ID of Upper Layer

Referring to FIG. 10, the temporal level ID of a current picture of anupper layer may be compared with the temporal level ID of acorresponding picture of a lower layer (S1000).

Specifically, it may be determined whether the temporal level ID of thecurrent picture of the upper layer and the temporal level ID of thecorresponding picture of the lower layer have the same value ordifferent values. If the current picture of the upper layer and thecorresponding picture of the lower layer have different temporal levelIDs, it may be inefficient to perform inter-layer prediction orinter-layer tile alignment.

Tile alignment between multiple layers may be performed based on aresult of the comparison of step S1000 (S1010).

Specifically, if the current picture of the upper layer and thecorresponding picture of the lower layer have different temporal levelIDs, inter-layer tile alignment may not be performed. On the other hand,if the current picture of the upper layer and the corresponding pictureof the lower layer have the same temporal level ID, inter-layer tilealignment may be performed.

(3) Use of Maximum Temporal Level ID of Lower Layer and Temporal LevelID of Upper Layer

Inter-layer tile alignment may be performed adaptively in theabove-described methods (1) and (2) combined.

Referring to FIG. 11, a maximum temporal level ID of a lower layer maybe acquired (S1100).

The maximum temporal level ID acquired in step S1100 may be comparedwith the temporal level ID of a corresponding picture of the lower layer(S1110).

If the temporal level ID of the corresponding picture of the lower layeris larger than the maximum temporal level ID of the lower layer in stepS1110, the corresponding picture of the lower layer may not be used asan inter-layer reference picture for a current picture of an upperlayer. Therefore, inter-layer tile alignment may not be performed on thecurrent picture of the upper layer based on the corresponding picture ofthe lower layer (S1120).

On the contrary, if the temporal level ID of the corresponding pictureof the lower layer is equal to or less than the maximum temporal levelID of the lower layer in step S1110, the temporal level ID of a currentpicture of an upper layer may be compared with the temporal level ID ofthe corresponding picture of the lower layer (S1130).

Tile alignment between multiple layers may be performed based on aresult of the comparison of step S1130 (S1140).

That is, if the current picture of the upper layer and the correspondingpicture of the lower layer have different temporal level IDs,inter-layer tile alignment may not be performed. On the other hand, ifthe current picture of the upper layer and the corresponding picture ofthe lower layer have the same temporal level ID, inter-layer tilealignment may be performed.

Meantime, while the temporal level IDs of the upper layer and the lowerlayer are compared after the maximum temporal level ID of the lowerlayer is compared with the temporal level ID of the correspondingpicture of the lower layer in FIG. 11, the comparison order is notlimited. It is obvious that after the temporal level IDs of the upperlayer and the lower layer are compared, the maximum temporal level ID ofthe lower layer may be compared with the temporal level ID of thecorresponding picture of the lower layer.

FIG. 12 is a flowchart illustrating a method for performing restrictedinter-layer prediction depending on inter-layer tile alignment ormisalignment in an embodiment to which the present invention is applied.

Referring to FIG. 12, it may be determined whether tiles have beenaligned between an upper layer and a lower layer (S1200).

For example, it may be determined whether tiles have been alignedbetween the upper layer and the lower layer based on a tile boundaryalignment flag, tile_boundaries_aligned_flag[i][j].

Specifically, if the value of the tile boundary alignment flag,tile_boundaries_aligned_flag[i][j] is 1, this implies that if twosamples of a current picture belonging to an i^(th) layer (i.e., theupper layer) belong to one tile, two samples of a corresponding picturebelonging to a j^(th) layer (i.e., the lower layer) belong to one tile,and if the two samples of the current picture belonging to the i^(th)layer (i.e., the upper layer) belong to different tiles from each other,the two samples of the corresponding picture belonging to the j^(th)layer (i.e., the lower layer) belong to different tiles from each other.

Therefore, if the value of the tile boundary alignment flag,tile_boundaries_aligned_flag[i][j] is 1, this may imply that tile sizesor tile units are aligned between the current picture of the upper layerand the corresponding picture of the lower layer. On the contrary, ifthe tile boundary alignment flag, tile_boundaries_aligned_flag[i][j] is0, this may imply that tiles are not aligned between the layers.

The j^(th) layer may be a layer having direct dependency on the i^(th)layer. It may be determined whether a layer has direct dependency on theupper layer based on a direct dependency flagdirect_dependency_flag[i][j]. The direct dependency flagdirect_dependency_flag[i][j] may indicate whether the j^(th) layer isused in inter-layer prediction of the i^(th) layer.

For example, if the value of the direct dependency flagdirect_dependency_flag[i][j] is 1, the j^(th) layer may be used ininter-layer prediction of the i^(th) layer, and if the value of thedirect dependency flag direct_dependency_flag[i][j] is 0, the j^(th)layer may not be used in inter-layer prediction of the i^(th) layer.

Meanwhile, a temporal level identifier of a corresponding pictureincluded in the j^(th) layer may be equal to or less than a maximumtemporal level identifier relating to the j^(th) layer. This matter hasbeen reviewed via FIG. 4 and FIG. 5, so details regarding this matterare omitted. Or, a corresponding picture included in a j^(th) layer mayhave a same temporal level identifier with a current picture included inan i^(th) layer.

Also, two samples of the corresponding picture belonging to the j^(th)layer may refer to samples at the same positions as two samples of thecurrent picture.

The tile boundary alignment flag, tile_boundaries_algned_flag[i][j] maybe acquired from Video Usability Information (VUI) in a video parameterset. The VUI may refer to information used for decoder conformance oroutput timing conformance.

Meanwhile, in the presence of information about the tile size or tileunit of at least one picture belonging to each of the upper layer (i.e.,the j^(th) layer) and the lower layer (i.e., the i^(th) layer), the tileboundary alignment flag, tile_boundaries_aligned_flag[i][j] may beacquired. A method for acquiring a tile boundary alignment flag will bedescribed with reference to FIGS. 13, 14, and 15.

Referring to FIG. 12, restricted inter-layer prediction may be performedbased on a result of the determination of step S1200 (S1210).

It may be restricted that a sample in a specific area of thecorresponding picture of the lower layer is not used for inter-layerprediction of the current picture of the upper layer according to thetile boundary alignment flag of the current picture of the upper layer.

Specifically, if the value of the tile boundary alignment flag of thecurrent picture is 1, it may be restricted that a sample outside a tileof the corresponding picture is not used for inter-layer prediction of asample inside a tile of the current picture. That is, if the value ofthe tile boundary alignment flag of the current picture is 1,inter-layer prediction may be performed on a sample inside a tile of thecurrent picture, only using a sample inside a tile of the correspondingpicture.

On the contrary, if the value of the tile boundary alignment flag of thecurrent picture is 0, the constraint that a sample outside a tile of thecorresponding picture is not used for inter-layer prediction of a sampleinside a tile of the current picture may not be applied. That is, if thevalue of the tile boundary alignment flag of the current picture is 0,inter-layer prediction may be performed on a sample inside a tile of thecurrent picture, using a sample inside and/or outside a tile of thecorresponding picture.

A tile of the current picture may refer to a tile matching a tile of thecorresponding picture through inter-layer tile alignment. Also, each ofthe tiles of the current picture and the corresponding picture may beone tile or a set of a plurality of tiles.

FIGS. 13, 14, and 15 illustrate syntaxes of a tile boundary alignmentflag in an embodiment to which the present invention is applied.

Referring to FIG. 13, the tile boundary alignment flag,tile_boundaries_aligned_flag[i][j] may be acquired (S1300).

As described before, the tile boundary alignment flag,tile_boundaries_aligned_flag[i][j] may indicate whether the tile size ortile unit of an i^(th) layer is aligned with the tile size or tile unitof a j^(th) layer. Herein, the j^(th) layer is a layer having directdependency on the i^(th) layer among a plurality of layers included in avideo sequence. That is, the j^(th) layer refers to a layer used forinter-layer prediction of the i^(th) layer. Accordingly, as many tileboundary alignment flags, tile_boundaries_aligned_flag[i][j] as thenumber NumDirectRefLayers_id_in_nuh[i] of layers having directdependency on the i^(th) layer may be acquired.

Meanwhile, inter-layer tile alignment may not be used for any of thelayers included in the video sequence. For this purpose, a non-tilealignment flag, tile_boundaries_non_aligned_flag may be signaled.

Referring to FIG. 14, the non-tile alignment flag,tile_boundaries_non_aligned_flag may be acquired (S1400).

The non-tile alignment flag, tile_boundaries_non_aligned_flag mayindicate whether inter-layer alignment is restricted in a layer of avideo sequence.

Specifically, if the non-tile alignment flag,tile_boundaries_non_aligned_flag is 1, a constraint that inter-layertile alignment is not performed on a layer of the video sequence isapplied.

For example, if a picture belonging to a layer of the video sequencedoes not use a tile, inter-layer tile alignment may not be performed.When a picture of the video sequence does not use a tile, the non-tilealignment flag, tile_boundaries_non_aligned_flag is encoded to be 1.When the non-tile alignment flag, tile_boundaries_non_aligned_flag is 1,this means that a picture of the video sequence does not use a tile andthe constraint that inter-layer tile alignment is not performed may beapplied.

On the contrary, if the non-tile alignment flag,tile_boundaries_non_aligned_flag is 0, this means that the constraintthat inter-layer tile alignment is not performed in a layer of the videosequence is not applied. For example, if the non-tile alignment flag,tile_boundaries_non_aligned_flag is 0, this means that a picturebelonging to the layer of the video sequence uses a tile. Also, if thenon-tile alignment flag, tile_boundaries_non_aligned_flag is 0, thismeans that inter-layer tile alignment may be performed in at least oneof the layers of the video sequence.

Therefore, the non-tile alignment flag, tile_boundaries_non_aligned_flagmay indicate whether the tile boundary alignment flag is present or thetile boundary alignment flag is extracted from a bit stream.

Referring to FIG. 14, only when the non-tile alignment flag,tile_boundaries_non_aligned_flag is 0, the tile boundary alignment flag,tile_boundaries_aligned_flag[i][j] may be acquired restrictively(S1410).

That is, if the non-tile alignment flag,tile_boundaries_non_aligned_flag is 1, inter-layer tile alignment is notperformed in any of the layers of the video sequence. Thus, there is noneed for signaling the tile boundary alignment flag,tile_boundaries_aligned_flag[i][j] indicating whether tile alignment isapplied, on a layer basis.

As described before with reference to FIG. 13, the tile boundaryalignment flag, tile_boundaries_aligned_flag[i][j] may indicate whetherthe tile size or tile unit of an i^(th) layer is aligned with the tilesize or unit of a j^(th) layer. Herein, the j^(th) layer is a layerhaving direct dependency on the i^(th) layer among a plurality of layersincluded in a video sequence. That is, the i^(th) layer refers to alayer used for inter-layer prediction of the i^(th) layer. Accordingly,as many tile boundary alignment flags,tile_boundaries_aligned_flag[i][j] as the numberNumDirectRefLayers_id_in_nuh[i] of layers having direct dependency onthe i^(th) layer may be acquired.

Meanwhile, it may occur that inter-layer tile alignment is used in allother layers except for a layer (e.g., a layer encoded by a H.264/AVC orHEVC codec) in which inter-layer prediction is not performed, in a videosequence. In this case, a tile alignment present flag(tile_boundaries_aligned_present_flag) indicating whether the tileboundary of all other layers may be derived may be signaled.

Referring to FIG. 15, a tile alignment presentflag(tile_boundaries_aligned_present_flag) may be acquired (S1500).

Here, the tile alignment present flag indicates whether a tile boundaryis derived on all other layers in a video sequence except for a layer inwhich inter-layer prediction is not performed.

For example, when the tile alignment present flag is 1, the tileboundary is derived for all other layers in a video sequence except fora layer in which inter-layer prediction is not performed. When the tilealignment present flag is 0, the tile boundary is not derived for allother layers in a video sequence except for a layer in which inter-layerprediction is not performed.

Therefore, only when the tile alignment present flag is 0, the tileboundary alignment flag(tile_boundaries_aligned_flag[i][j]) may beacquired restrictively (S1510).

That is, if the tile alignment present flag is 1, this means that thetile boundary belonging to a picture or a slice is derived. Thus, thereis no need for signaling the tile boundary alignment flag on a layerbasis. On the contrary, if the tile alignment present flag is 0, thetile boundary belonging to a picture or a slice is not derived. Thus,there is need for signaling the tile boundary alignment flag indicatingwhether the tile alignment is applied, on a layer basis.

Specifically, whether the tile boundary belonging to a picture or aslice is derived may be determined based on the number of a tilebelonging to the picture or the slice.

For example, if the number of a tile belonging to the picture of thevideo sequence is 1, this means that one tile belonging to the pictureis the same as the picture. In other words, this also means the picturedoes not use a tile. In this case, the tile boundary may be derived tobe equal to the picture boundary. Therefore, if the number of a tilebelonging to the picture of the video sequence is 1, the tile alignmentpresent flag may be encoded to be 1 and the tile boundary present flagmay not be signaled on a layer basis. The tile boundary present flag maynot be acquired when the number of a tile belonging to the picture ofthe video sequence is 1.

Whereas, if the number of a tile belonging to the picture of the videosequence is two or more, there is need for signaling the tile boundaryalignment flag on a layer basis since the tile boundary is not derived.That is, the tile boundary alignment flag may be acquired when thenumber of a tile belonging to the picture of the video sequence is twoor more. Here, the case that the number of a tile belonging to thepicture of the video sequence is two or more 1 means that the pictureuses a tile.

The tile boundary alignment flag(tile_boundaries_aligned_flag[i][j]) mayindicate whether an i^(th) layer is aligned with the tile size or tileunit of a j^(th) layer. Herein, the j^(th) layer is a layer havingdirect dependency on the i^(th) layer, among a plurality of layersincluded in a video sequence. That is, the j^(th) layer refers to alayer to be used for inter-layer prediction of the i^(th) layer.Accordingly, as many tile boundary alignment flags as the number(NumDirectRefLayers_id_in_nuh[i]) of layers having direct dependency onthe i^(th) layer may be acquired.

FIG. 16 is a flowchart illustrating a method for up-sampling acorresponding picture of a lower layer in an embodiment to which thepresent invention is applied.

Referring to FIG. 16, the position of a reference sample of a lowerlayer corresponding to the position of a current sample of an upperlayer may be derived (S1600).

Since the upper layer and the lower layer may have differentresolutions, the position of the reference sample of the lower layercorresponding to the position of the current sample of the upper layermay be derived in consideration of the difference between theresolutions of the layers. That is, the width-height ratios of picturesof the upper layer and the lower layer may be taken into account. Also,the size of an up-sampled picture of the lower layer may not match thesize of the picture of the upper layer, and thus an offset forcorrecting the size difference may be required.

For example, the position of the reference sample may be determined,taking into account a scale factor and an up-sampled lower layer offset.

The scale factor may be calculated based on the width-height ratios ofthe current picture of the upper layer and the corresponding picture ofthe lower layer.

The up-sampled lower layer offset may refer to information about thedifference between the position of a sample at an edge of the currentpicture and the position of a sample at an edge of the inter-layerreference picture. For example, the up-sampled lower layer offset mayinclude information about a horizontal/vertical-directional differencebetween the position of a sample at a top left end of the currentpicture and the position of a sample at a top left end of thecorresponding picture, and information about ahorizontal/vertical-directional difference between the position of asample at a bottom right end of the current picture and the position ofa sample at a bottom right end of the corresponding picture.

The up-sampled lower layer offset may be acquired from a bit stream. Forexample, the up-sampled lower layer offset may be acquired from at leastone of a video parameter set, a sequence parameter set, a pictureparameter set, or a slice header.

A filter coefficient of an up-sampling filter may be determined inconsideration of the phase of the reference sample position determinedin step S1600 (S1610).

Herein, either of a fixed up-sampling filter and an adaptive up-samplingfilter may be used as the up-sampling filter.

1. Fixed Up-sampling Filter

A fixed up-sampling filter may refer to an up-sampling filter having apredetermined filter coefficient, with no regard to the characteristicsof a video. A tap filter may be used as the fixed up-sampling filter,and a fixed up-sampling filter may be defined for each of a luminancecomponent and a chrominance component. With reference to [Table 1] and[Table 2], fixed up-sampling filters having an accuracy of a 1/16 sampleunit will be described.

TABLE 1 Coefficients of interpolation filter Phase f[p, f[p, f[p, f[p,f[p, f[p, f[p, f[p, p 0] 1] 2] 3] 4] 5] 6] 7] 0 0 0 0 64 0 0 0 0 1 0 1−3 63 4 −2 1 0 2 −1 2 −5 62 8 −3 1 0 3 −1 3 −8 60 13 −4 1 0 4 −1 4 −1058 17 −5 1 0 5 −1 4 −11 52 26 −8 3 −1 6 −1 3 −3 47 31 −10 4 −1 7 −1 4−11 45 34 −10 4 −1 8 −1 4 −11 40 40 −11 4 −1 9 −1 4 −10 34 45 −11 4 −110 −1 4 −10 31 47 −9 3 −1 11 −1 3 −8 26 52 −11 4 −1 12 0 1 −5 17 58 −104 −1 13 0 1 −4 13 60 −8 3 −1 14 0 1 −3 8 62 −5 2 −1 15 0 1 −2 4 63 −3 10

[Table 1] defines filter coefficients for a fixed up-sampling filter,for the luminance component.

As noted from [Table 1], an 8-tap filter is applied for up-sampling ofthe luminance component. That is, interpolation may be performed using areference sample of a reference layer corresponding to a current sampleof the upper layer and samples adjacent to the reference sample. Theadjacent samples may be specified according to an interpolationdirection. For example, if interpolation is performed in a horizontaldirection, the adjacent samples may include three consecutive samples tothe left of the reference sample and four consecutive samples to theright of the reference sample. Or if interpolation is performed in avertical direction, the adjacent samples may include three consecutivesamples above the reference sample and four consecutive samples underthe reference sample.

Since interpolation is performed with an accuracy of a 1/16 sample unit,there are a total of 16 phases, for supporting resolutions of variousmagnifications such as 2 times, 1.5 times, etc.

Further, the fixed up-sampling filter may use a different filtercoefficient for each phase p. Except for a case of a phase of 0 (p=0),the size of each filter coefficient may be defined to be within a rangeof 0 to 63. This means that filtering is performed with an accuracy of 6bits. The phase of 0 means the positions of integer samples, the integerbeing a multiple of n, if interpolation is performed in units of a 1/nsample.

TABLE 2 Coefficients of interpolation filter Phase p f[p, 0] f[p, 1]f[p, 2] f[p, 3] 0 0 64 0 0 1 −2 62 4 0 2 −2 58 10 −2 3 −4 56 14 −2 4 −454 16 −2 5 −6 52 20 −2 6 −6 46 28 −4 7 −4 42 30 −4 8 −4 36 36 −4 9 −4 3042 −4 10 −4 28 46 −6 11 −2 20 52 −6 12 −2 16 54 −4 13 −2 14 56 −4 14 −210 58 −2 15 0 4 62 −2

[Table 2] defines filter coefficients for a fixed up-sampling filter,for the chrominance component.

As noted from [Table 2], a 4-tap filter is applied for up-sampling ofthe chrominance component, compared to the luminance component. That is,interpolation may be performed using a reference sample of a referencelayer corresponding to a current sample of the upper layer and samplesadjacent to the reference sample. The adjacent samples may be specifiedaccording to an interpolation direction. For example, if interpolationis performed in the horizontal direction, the adjacent samples mayinclude one consecutive sample to the left of the reference sample andtwo consecutive samples to the right of the reference sample. Or ifinterpolation is performed in the vertical direction, the adjacentsamples may include one consecutive sample above the reference sampleand two consecutive samples under the reference sample.

Since interpolation is performed with an accuracy of a 1/16 sample unitas in the case of the luminance component, there are a total of 16phases, and the fixed up-sampling filter may use a different filtercoefficient for each phase p. Except for a case of a phase of 0 (p=0),the size of each filter coefficient may be defined to be within a rangeof 0 to 63. This means that filtering is performed with an accuracy of 6bits.

While it has been described above that an 8-tap filter and a 4-tapfilter are applied respectively to the luminance component and thechrominance component, the present invention is not limited thereto.Obviously, the order of a tap filter may be determined variably inconsideration of coding efficiency.

2. Adaptive Up-sampling Filter

An encoder may determine an optimum filter coefficient in considerationof the characteristics of a video without using a fixed filtercoefficient, and signal the determined filter coefficient to a decoder.In this manner, an adaptive up-sampling filter uses a filter coefficientadaptively determined by the encoder. Since a video has a differentcharacteristic on a picture basis, use of an adaptive up-sampling filterthat represents well the characteristics of the video instead of using afixed up-sampling filter for all cases may lead to improved codingefficiency.

An inter-layer reference picture may be generated by applying the filtercoefficient determined in step S1610 to a corresponding picture of thelower layer (S1620).

Specifically, interpolation may be performed by applying the determinedfilter coefficient for the up-sampling filter to samples of thecorresponding picture. Herein, the interpolation may be performedprimarily in the horizontal direction and secondarily on samplesgenerated from the horizontal interpolation in the vertical direction.

INDUSTRIAL APPLICABILITY

The present invention may be used in encoding/decoding a video signal ofa multi-layer structure.

The invention claimed is:
 1. A method for decoding a multi-layer videosignal with a decoding apparatus, the method comprising: determining,with the decoding apparatus, whether a corresponding picture of a lowerlayer is used in inter-layer prediction of a current picture of an upperlayer, based on a temporal level identifier (ID) of the lower layer; andperforming, with the decoding apparatus, inter-layer prediction of thecurrent picture using the determined corresponding picture of the lowerlayer, if the corresponding picture of the lower layer is used ininter-layer prediction of the current picture of the upper layer,wherein a tile alignment present flag is obtained from a bitstream whenvideo usability information is presented in the bitstream, when the tilealignment present flag equals to 1, the tile alignment present flagindicates that a first restriction is applied, and when the tilealignment present flag equals to 0, the tile alignment present flagindicates that the first restriction may or may not be applied, wherethe first restriction is to restrict all pictures belonging to a videosequence to consist of a single tile, wherein a tile boundary alignmentflag is obtained from the bitstream when the tile alignment present flagis equal to 0, when the tile boundary alignment flag equals to 1, thetile boundary alignment flag indicates that a second restriction isapplied, and when the tile boundary alignment flag equals to 0, the tileboundary alignment flag indicates that the second restriction may or maynot be applied, wherein the second restriction is to restrict i) twosamples of a corresponding picture of the lower layer to belong to onetile when two samples of the current picture of the upper layer belongto one tile, and ii) the two samples of the corresponding picture of thelower layer to belong to different tiles when the two samples of thecurrent picture of the upper layer belong to different tiles, whereinthe determined corresponding picture of the lower layer is a picture towhich a 8-tap filter is applied for performing inter-layer prediction onthe current picture, wherein coefficients of the 8-tap filter are {0, 1,−3, 8, 62, −5, 2, −1}, and wherein when the corresponding picture isused for inter-layer prediction of a current block of the currentpicture, both x and y components of a motion vector relating to thecurrent block are derived equal to zero.